Several small toroidal inductors. The major scale is in inches.
A small toroidal transformer.
Toroidalinductors and transformers are a kind of electronic component. They typically consist of a circular, ring-shaped magnetic centre. The magnet is usually considered a monopole, although the central axis will have a dipole, and have the advantage of being wound continuously in a single direction, thus there is no inductive interference between windings as in a solenoid that is wound back and forth.